Unconfirmed reports say troops were sent to deal with a new coup attempt.
The base at Incirlik, home to almost 3,000 US troops, was placed on high alert - Force Protection Condition Delta - last week after a faction of Turkish military officers tried to overthrow the government.
The Incirlik air base, located in an urban neighborhood in the southern Turkey city of Adana, reopened following a meeting with "security officials".
We did the general security check.
Turkish authorities restored access to and from the key United States air base early Sunday, local media reported, the day the USA top military official is scheduled to visit the country and tour the base.
Activists chanted anti-American slogans and called on citizens to join such protest.
Speaking in an interview with ATV and A Haber channels, Erdogan said the moves aim to bring the Turkish military under civilian control after the failed coup attempt last month.
It houses U.S. tactical nuclear missiles. Incirlik air base is used by U.S. and North Atlantic Treaty Organisation forces to launch air strikes and drone attacks on Syria and Iraq. The exact number of nuclear bombs kept at the base is unknown, although, according to various estimates, it may store up to 90 warheads.
The cut off of Incrilik airbase is the second times in recent weeks that Turkey has been willing to hold the airbase hostage in return for favorable policies or rhetoric from the U.S. In the immediate week after the coup, Turkey cut off the power to Incrilik airbase for almost a week, prompting concern among U.S. policymakers.
The inspection at the base comes as the Turkish government announced a sweeping military reform on Saturday.
Witnesses at the scene took photos of Turkish forces armed with rifles and riding in armored TOMA vehicles. Diplomatic sources quoted by Hurriyet claim Dunford will visit both Ankara and Incirlik.